Effects of Training Against Elastic Resistance on Jab Punch Performance in Elite Junior Athletes

Markovic, P. et al.: EFFECTS OF TRAINING AGAINST ELASTIC RESISTANCE... Kinesiology 48(2016)1:79-86

EFFECTS OF TRAINING AGAINST ELASTIC RESISTANCE ON JAB PUNCH PERFORMANCE IN ELITE JUNIOR ATHLETES

Predrag Markovic1, Dejan Suzovic1, Goran Kasum1, and Slobodan Jaric2 1The Research Center, Faculty of Sport and Physical Education, University of Belgrade, Serbia 2Department of Kinesiology and Applied Physiology & Biomechanics and Movement Science Graduate Program, University of Delaware, Newark, USA

Original scientific paper UDC: 796.8:796.012.13

Abstract: Ability to perform rapid open-kinetic chain movements (e.g. kicking, throwing, hitting, or punching) is an important prerequisite for success in various sports. The aims of the present study were (1) to investigate the effect of elastic resistance training (ERT) on the performance of jab punch, (2) to explore the associated changes in movement kinematic and kinetic patterns, and (3) to assess possible differences among competitors of different specializations. The national level junior competitors in kick boxing, savate, and boxing practiced jab punch against elastic resistance for 15 minutes per day, 3 times a week for 6 weeks, while the control group participated only in their regular training (N=10+10+10+10; age 17.2±1.0 years; M±SD). The results revealed a marked increase in the maximum jab punch velocity in all experimental groups (6-11%; all p<.01), but not in the control group (p>.05). This finding was associated with an increase in both the maximum velocity and displacement of the ipsilateral elbow, shoulder, and, particularly, hip joint, while no change in the movement time was observed. The ERT-associated increase was also revealed in the agonist (7-11%, all p<.01), but not antagonist muscle strength. Therefore, we conclude that addition of a relatively small amount of ERT could be recommended for the purpose of improving punching performance and, possibly, other rapid limb movement even in top-level junior athletes. The observed performance improvement could be partly based on increased motion amplitudes particularly regarding the pelvis movement, as well as on increased strength of agonist muscles.

Key words: open kinetic chain, movement, velocity, displacement, strength, martial arts

Introduction upper-body training led for improving throwing Standard strength training programs for athletes performance (Prokopy, et al., 2008). typically combine closed- and open-kinetic chain Proximal-to-distal sequences (Cabral, João, exercises to improve the core upper- and lower-body Amado, & Veloso, 2010) of individual body segments was observed in throwing, striking, strength, sport-speciﬁc strength, and performance, or kicking movements performed in variety of as well as for injury prevention (Prokopy, et al., sports, often with the aim to maximize velocity 2008). Closed-kinetic chain exercises require ﬁxing of the end- point (Marshal & Elliott, 2000). For the distal segment or providing it with a consider- example, the peak linear and angular velocities were able resistance (Steindler, 1955), such as the hands found to progress from the trunk to the wrist in a pushing against the ground during a push-up. Open- squash forehand stroke and the segmental veloci- kinetic chain exercises allow the end- point to move ties increased progressively throughout the kine- freely either with or without external resistance, matic chain (Woo & Chapman, 1994). Baseball such as when performing punches, throws or kicks, players accelerate the elbow and wrist joint rota- or exercising with free weights (West, Cunningham, tions by utilizing the velocity-dependent torque Crewther, Cook, & Kilduff, 2013). Since the kine- that is originally produced by the proximal trunk matic patterns typical for rapid movements of open- and shoulder joint torques (Hirashima, Yamane, kinetic chains are known to maximize the end-point Nakamura, & Ohtsuki, 2008), while the peak pelvic velocity, such movements were favored by coaches angular velocity during the volleyball spike perfor- for the purpose of upper-body training (Dillman, mance precedes the shoulder external rotation and Murray, & Hintermeister, 1994). Nevertheless, both contribute to a higher ball speed (Dunbar, other studies recommended the closed-kinetic chain Chmielewski, Tillman, Zheng, & Conrad, 2012).

79 Markovic, P. et al.: EFFECTS OF TRAINING AGAINST ELASTIC RESISTANCE... Kinesiology 48(2016)1:79-86

This all lead to a conclusion that to understand the The use of ERT methods for improving kicking mechanisms in performance improvement of the performance was already recommended (Davies, movements such as throwing, striking, or kicking, 2003). However, there were few studies aimed at the role of all open-kinetic chain body segments examining the effects of ERT on other rapid open- need to be explored. kinetic chain movements. For example, effective- Punching movements, typical for many combat ness of ERT in improvement of serving speed in sports and martial arts, represent a typical example elite tennis players was demonstrated (Treiber, et of the open-kinetic chain movements where the al., 1998), while a study conducted on taekwondo main task is to maximize hand velocity as the main competitors revealed similar results regarding the performance variable. For example, the straight jab improvement in the kick velocity (Jakubiak, et al., punch, thrown by the lead hand in boxing (also 2008). However, the mechanisms involved in the known as reverse punch in karate) is a fundamental, improvement of open-kinetic chain performance score-making, and powerful skill (Cheraghi, associated with ERT remain largely unknown. Alinejad, Arshi, & Shirzad, 2014). The magnitude Among the candidates could be both the training- of force exerted at the point of impact is governed by associated changes in muscle strength and/or move- a number of factors, among which are: force gener- ment kinematic and kinetic patterns. Signifcant ated by the legs (Filimonov, Koptsev, Husyanov, & correlations have been found between muscle Nazarov, 1985), degree of body rotation, and the torque and punch force in boxers that emphasizes distance over which the punch is thrown (Hickey, a possible role of muscle strength in movement 1980). The trajectory of the hand in the anterior- performance (Karpiłowski, Nosarzewski, Staniak, posterior direction indicates a higher velocity in a & Trzaskoma, 2001). However, the possible changes throwing phase than that portrayed in a returning in the movement kinematic patterns remain largely phase. Hip anterior displacement represents a underexplored. weight shift toward intended direction of the punch. To address the discussed problems, the frst aim Nevertheless, the role of particular segments and the of our study was to explore the effectiveness of ERT involved muscle groups in punching still remains on jab punching in young individuals with already unresolved, which inevitably constrains devel- a high level of the movement performance. Specif- opment of training methods aimed at improving ically, we introduced a moderate amount of ERT performance. One of the reasons for that is that to elite junior athletes in addition to their regular the punching techniques could considerably differ training. Our second aim was to explore the changes both within and across various martial arts and in movement kinematic pattern that could have combat sports, such as boxing, karate, taekwondo, contributed to the expected improvement in move- or kickboxing (Marshal & Elliot, 2000; Cohran, ment performance. Specifcally, we explored the 2003; Cabral, et al., 2010, Loturco, Artioli, Kobal, training-associated changes in both the velocity and Gil, & Franch, 2014). displacement of selected body segments of the tested Regarding the training interventions aimed open-kinetic chain. Our third aim was to explore at improving performance of rapid and explosive the possible differences in both the effectiveness open-kinetic chain movements, the transferability of the ERT training and the changes in kinematic of strength gains achieved from general resistance patterns among the athletes of different specializa- training methods to sport-specifc performance tion. Findings of the present study could contribute still remains unclear (Hetzler, et al., 1997; Newton, not only to refnement of training procedures aimed Kraemer, & Hakkinen, 1999). It has been often at improving jab punching and other rapid open- recommended that a higher training transfer to the kinetic chain movements performance, but also to actual performance could be achieved from exer- advancing our understanding of the mechanisms cises based on the specifc movements performed in involved in the performance improvement. competition (Stone, Plisk, & Collins, 2002; Kane- hisa & Miyashita, 1983). The specifc strength Methods training programs often used ballistic movements with medicine balls (Szymanski, Szymanski, Brad- Experimental approach to the problem ford, Schade, & Pascoe, 2007; Ignjatovic, Markovic, To assess the effects of moderate amount of & Radovanovic, 2012; van den Tilaar & Marques, elastic resistance training (ERT) on both the 2009, 2013), dumbbells and barbells (West, et improvement in punching performance and the al., 2013; Marques, van den Tilaar, Vescovi, & involved mechanisms, three experimental and Gonzalez-Badillo, 2007), as well as the elastic one control group of junior elite athletes of partly resistance training (ERT) methods (Davies, 2003; different combat sport specializations were tested Treiber, Lott, Duncan, Slavens, & Davis, 1998; both prior to and after 6 weeks of ERT. In addition Dinn, & Behm, 2007; Jakubiak, & Saunders, 2008). to the peak velocity of hand as the main perfor- The exercises based on ERT also found applica- mance variable, the associated changes in kine- tion in the recovery and rehabilitation of athletes matic patterns of other elements of the tested open- (Ellenbecker, Pluim, Vivier, & Sniteman, 2009). kinetic chain was assessed by peak velocities and

80 Markovic, P. et al.: EFFECTS OF TRAINING AGAINST ELASTIC RESISTANCE... Kinesiology 48(2016)1:79-86 displacements of the elbow, shoulder and hip joint. Four tightly secured reflecting markers were To assess a possible role of muscle strength in the placed at the subjects’ body to record joint motion tested movement performance, the training-associ- of specifc joints (see Figure 1). Specifcally, they ated changes in strength of elbow flexors and exten- were placed over the bony landmarks of their domi- sors were also evaluated. nant side wrist (styloid process of the radius), elbow (lateral epicondyle of humerus), shoulder (acromion Subjects process), and hip (anterior superior iliac spines). The participants (N=40) were experienced A three-camera motion capture system (ProReflex junior male athletes that were active in the infrared, Qualisys 3D), sampling at a frame rate of following combat sports: kick boxing (KB; n=14), 240 Hz, was applied to capture velocity and range savate boxing (SB; n=13) and boxing (BO; n=13). of motion of wrist, elbow, shoulder, and hip joints They were assigned to three experimental groups during the jab punch performance. The capture according to their specialization (10 subjects system was positioned at the lateral body side to each), while the control group (n=10) consisted of avoid covering the markers by other body segments randomly selected remaining 3 KB, 4 SB and 3 over the course of testing. The standard commercial BO athletes. All participants were the national level software (Qualisys Track Manager; QTM) for 3D competitors, as well as members of the national motion capture was used to record 3D coordinates junior teams. Their age (M±SD) was 17.2±1.0 years, of the markers. The between-day reliability of kine- body height: 1.79±0.07 m, and body mass: 72.8±7.5 matic variables obtained using a similar approach kg. No signifcant differences in either the body proved to be high (Brian, Manal, & Davis, 2010). size or age were observed among the groups (all p>.1). Their training experience was between 5.0 and 9.5 years, and at the time of the study all of them were involved in their regular training protocols implemented between 6.0 and 10.5 hours per week. The protocols did not involve any kind of resistance training. All participants were healthy and in good physical condition. None reported injuries or illnesses that could compromise the tested performance, neither they had had previous experience with ERT. The study was approved by the local IRB and written assents were obtained from all participants Figure 1. Illustration of the initial (left hand side) and final as well as from their parents prior to any testing. body posture (right hand side) together with the position of the attached reflected markers (empty circles) Experimental protocol The testing was conducted prior to (i.e. the Muscle strength test pretest) and three days after a 6-week training To assess a possible training-associated increase period (posttest). Both the pretest and posttest in the strength of muscles acting against the applied consisted of a single session aimed to test the resistance and contrast it with their antagonists, we maximal velocity and displacement of tracked selected the elbow extensor and flexor muscle and joints, as well as to assess the elbow extensor and tested their maximum isometric force (Abernethy, flexor muscles’ strength. The pretest was preceded Wilson, & Logan, 1995; Jaric, 2002). The apparent by anthropometric measurements where body mass candidates for this selection were also the shoulder, and height were assessed by a digital scale and a hip, and knee extensors and flexors, but we believed standard kinanthropometer, respectively. that elbow muscles, being the weakest, could be most exposed to the applied resistive force. The Jab punch testing test was conducted on the elbow flexor and extensor Following a standard stretching and warm-up muscles by means of a standard Kin-Com isoki- procedure consisting of fve minutes cycling and netic dynamometer (Chatex Corp., Chattanooga, 10 minutes of callisthenics and dynamic stretching, TN) set to static condition. The subject was fxed the subjects were instructed to perform jab punches to the dynamometer by wide tight straps according to boxing punch mitts, all in the same stance (the to manufacturer recommendations. The axis of the non-dominant leg leading). The target was adjusted dynamometer was aligned with the elbow joint axes for individual boxers to their preferred height and set to 120° (180º being full extension). The subjects distance to address the task constraint of delivering were instructed to rapidly exert the maximum force their best dominant hand jab punch to a level of the against the band attached to the dominant forearm imagined opponent head. Subjects were instructed and to retain it for 3-4 s (Wilson & Murphy, 1996). to throw punch as fast as they could. The extensor and flexor muscles were tested in

81 Markovic, P. et al.: EFFECTS OF TRAINING AGAINST ELASTIC RESISTANCE... Kinesiology 48(2016)1:79-86 random sequence. On-line feedback regarding the Statistical analysis current force level was shown at a computer monitor Descriptive statistics were calculated for all positioned in front of the subject and verbal encour- dependent variables as means and SD. There- agement was provided. Three consecutive trials after, a series of mixed model 2-way ANOVAs were performed with 2-minute rests and the trial with the main effects of time (2 levels) and group with the highest force was taken for further analysis (4 levels) were conducted on individual variables as the measure of strength. with Boferroni post-hoc test for planned contrasts. The Cohen’s effect size (ES) was also calculated Training and the values of 0.2, 0.5, and 0.8 were considered The same training intervention was added to as small, moderate, and large effects, respectively. regular training routine of all subjects of the three Alpha was set to 0.05. experimental groups. The program of ERT was applied three times a week for six weeks. Specif- Results cally, the subjects performed six sets of ten repetitions of jab punch each with the instruction to Subjects of three experimental groups had reach the target (i.e. boxing punch mitts) as fast as 100% attendance of ERT, as well as a 100% compli- possible. ance with the prescribed number of ERT sets and The rest intervals between two consecutive repetitions. Training with elastic resistance did trials were 10 s and subjects rested between 45 and not contribute to visible distortion of their move- 60 s between the sets. Each session was conducted ment technique, as observed by experienced boxing at the end of their regular training session and lasted coaches. approximately 15 minutes. Figure 2 shows the kinematic variables observed The applied elastic resistance was same for all in the pretest and posttest and averaged across the subjects. It originated from rubber bands (resting subjects of all 4 groups. The upper panel depicts length 1.5 m, coeffcient of elasticity 133 N/m) with the values of Vpeak. Arguably, the most important one end externally fxed behind the subject, while individual variable is Vpeak of the wrist that repre- the subject held the other end by his punching hand. sents the main task variable. The applied 2-way Initially, the bands were pre-stretched about 15cm at ANOVA revealed a signifcant time-group interac- the starting hand position. Since the hand displace- tion (F=21, p<.01; ES=.64), as well as the signif- ment was on average about 90cm, the resisting cant main effect of time (F=213, p<.01; ES=0.86), elastic force increased from approximately 20N but not of the group (F=2.3, p>.05; ES=.16). Similar to 140N (i.e. between the starting and fnal hand fndings were observed for Vpeak in the remaining position). The resistive force was progressively 3 joints. Namely, Vpeak of the elbow also revealed a increased by adding 20cm of a pre-stretch per week signifcant time-group interaction (F=11.5, p<.01; which resulted in about 26.5N increase in resistance ES=.49), a signifcant main effect of time (F=99, (see Jakubiak, et al. 2008, for similar approach). p<.01; ES=.73), but not of the group (F=1.4, p>.05; Therefore, resistive force during the last week of ES=.11). Vpeak of the shoulder also revealed a signif- training ranged approximately between 150N and cant time-group interaction (F=17, p<.01; ES=.59), 270N. the signifcant main effect of time (F=167, p<.01; ES=.82), but not of the group (F=2.1, p>.05; ES=.15).

Data analyses Finally, Vpeak of the hip revealed a signifcant time- The signals from the cameras were sampled at group interaction (F=4.6, p<.01; ES=.28), the signif- a rate of 240 per second and fltered by a second- icant main effect of time (F=41, p<.01; ES=.53), but order Butterworth recursive low pass flter (10Hz not of the group (F=2.0, p>.05; ES=.14). The general cut-off frequency). A custom-designed Lab VIEW fnding across the tested variables is that Bonfer- (National Instruments, Version 8.2) program was roni post-hoc test showed signifcant increase in used to calculate the scalar values of 3D position Vpeak between the pre- and posttest in all four joints and velocity of each marker. The analyzed time of the three experimental groups, but not in the interval began at the frst visible initiation of the control group. wrist movement (i.e. when it reached 3% of its Regarding the observed changes in the displace- maximum velocity) and lasted until the hand’s ment, Disp of the wrist showed a signifcant time- impact with the boxing punch mitts set as a target. group interaction (F=6.0, p<.01; ES=.33), the signif-

It allowed for the calculation of peak velocity (Vpeak) icant main effect of time (F=61, p<.01; ES=.63), and displacement (Disp) of the reflecting markers but not of the group (F=.3, p>.05; ES=.02). Disp of placed at the hip, shoulder, elbow and wrist joints, the elbow revealed a signifcant time-group inter- as well as for the assessment of movement perfor- action (F=7.0, p<.01; ES=.37), the signifcant main mance time. The standard test provided information effect of time (F=67, p<.01; ES=.65), but not of the on strength of the elbow extensor (Fext) and flexor group (F=.3, p>.05; ES=.02). Disp of the shoulder (Fflx) muscles. also revealed a signifcant time-group interaction

82 Markovic, P. et al.: EFFECTS OF TRAINING AGAINST ELASTIC RESISTANCE... Kinesiology 48(2016)1:79-86

Pretest Posttest

Figure 2. Peak velocity (top panel) and displacement (bottom panel) observed in 4 joints in the pre- and posttest in four groups (data averaged across the subjects with SD error bars; * p<.05, paired t-test).

(F=7.6, p<.01; ES=.39), the signifcant main effect 202±17ms in CG. Of importance here is that none of time (F=59, p<.01; ES=.62), but not of the group of the differences was signifcant (all p>.1; one- (F=.1, p>.05; ES=.01). Only Disp of the hip revealed group t-test). both the signifcant time-group interaction (F=25, Finally, Figure 3 shows the data obtained from p<.01; ES=.67), and the main effects of both the time the elbow extensor and flexor muscle expected to (F=154, p<.01; ES=.81) and group (F=4.8, p<.01; assess the training-associated increase in muscle ES=.28). Collectively, similar to Vpeak, Disp showed strength. The elbow extensor revealed the signif- a signifcant increase in Vpeak between the pre- and cant main effect of time (F=150, p<.01; ES=.81), but posttest in all four joints of all experimental groups, not of group (F=2.4, p>.05; ES=.17), and a signif- but not in the control group. The only exception cant time-group interaction (F=13, p<.01; ES=.51). was the shoulder Disp obtained from KB group that Strength signifcantly increased in all the exper- remained somewhat below the Bonferroni corrected imental, but not in the control group. Regarding p=.0125. the elbow flexor, the results revealed neither the A potentially important fnding could origi- main effects of time (F=1.9, p<.01; ES=.05) or group nate from the comparisons in the changes observed (F=.8, p>.05; ES=.07), nor their interaction (F=.7, across the joints (see Figure 2 for the data). However, p>.05; ES=.06). since the results are obtained by 2-way ANOVAs originated from individual variables and joints, they do not allow for such comparisons. Nevertheless, Pretest note that the qualitative analysis suggests that the Posttest training-associated relative increase in Disp is markedly more pronounced in the hip than in other joints. That is reflected both in the highest ES of the time- group interaction and in the relative increase in Disp of about 40% in all the three experimental (but not in the control) groups. The increase in the other three joints is typically less than 10%. Another fnding of potential importance is the effect of ERT on movement time. Specif- cally, the data revealed movement time observed in the pre- and posttest was, respectively, 197±26 Figure 3. Strength of elbow extensors and flexors observed in and 192±29ms in KB, 206±32 and 215±23ms in the pre- and posttest in four groups (data averaged across the SB, 214±24 and 217±38ms in BO, and 200±16 and subjects with SD error bars; * p<.05, paired t-test).

83 Markovic, P. et al.: EFFECTS OF TRAINING AGAINST ELASTIC RESISTANCE... Kinesiology 48(2016)1:79-86

Discussion and conclusions responsible for the discussed performance improve- Within the present study we evaluated the effec- ment could be increased muscle strength. Although tiveness of ERT in performance improvement of we selected only one muscle group, note that while rapid open-kinetic chain movements. Specifcally, the agonist (i.e. elbow extensors) revealed a marked we tested the jab punch of elite junior athletes strength increase of 7-10%, the antagonist strength competing in different combat sports. Regarding increase was virtually zero. This result is in line the frst aim of the study, we found that a relatively with numerous studies of the effects of external small amount of ERT could result in a signif- load on the agonist-antagonist activity in single- cant increase in hand peak velocity in athletes of joint movements (Dinn, et al., 2007; Ignjatovic, et different specializations. Regarding the second aim, al., 2012). Specifcally, it is known for decades that among the mechanisms involved in the performance while an increased inertial load (e.g. added weight) increase could be a markedly increased displace- requires increased activity of both the agonist and ment of individual joints, particularly pronounced in antagonist (i.e. to propel and, thereafter, to termi- the hip, as well as an increase in the agonist but not nate the movement), an increase in elastic resisting antagonist muscle strength. However, despite the force (such as the applied ERT) requires only increased displacement, movement time remained increased agonist activity, since the applied resist- unchanged. Regarding our third aim, we did not ance acts as an antagonist per se (Hoffman & Strick, fnd any differences in any of the ERT-associated 1993). Nevertheless, the relative contribution of two changes. discussed mechanisms to the observed performance The main fnding of the study is an ERT- enhancement (i.e. the altered movement kinematic associated increase in movement performance pattern and increased muscle strength) certainly deserve attention of future studies. as assessed by the wrist peak velocity (Vpeak; see Figure 2). Of particular importance could be that The effects of applied ERT appeared to be the fnding was observed in individuals who were similar across the three experimental groups. In already both highly selected and trained for that addition to a possible lack of statistical power to particular movement performance. Moreover, the detect possible differences, one could also speculate effect was pronounced despite subjecting the partic- that the lack of the discussed differences originates ipants to only about 45 minutes of ERT training from similarities in the tested groups. Namely, all per week, that on average represented about 10% the three experimental groups were both selected of their total training time. Note also that although and trained in a relatively similar way. However, the movement distance (as assessed by Disp of the while one could presume that the jab punch tech- wrist) increased, the total movement time remained nique was also similar across the groups, note also approximately unchanged. This brings an apparent that moderate differences in the performance (i.e. advantage to various combat sports and martial arts Vpeak of the wrist) were observed among them. since the athlete is able to reach to his/her oppo- Several limitations of the present study, as nent from a more remote position over the same well as the directions for future research need to movement time (Dunbar, et al., 2012; Hirashima, et be recognized. First, of considerable importance al., 2008; Jakubiak & Saunders, 2008). Therefore, could be that the observed effectiveness of ERT was one could conclude that ERT may be highly effec- obtained from only one type of open-kinetic chain tive in increasing performance of rapid arm move- movement. Therefore, the applied training program ments such as the tested jab punch and, perhaps, should be evaluated on other rapid open-kinetic other open-kinetic chain movements (Davies, 2003; chain movements, such as on throwing or kicking. Jakubiak & Saunders, 2008). Second, future studies should conduct a more elabo- Of particular importance for the main fnding rate exploration of the mechanisms involved in the discussed in the previous paragraph could be the observed performance enhancement. For example, mechanisms involved in the observed performance the possible changes in movement patterns asso- improvement. The kinematic data suggest that an ciated with ERT could deserve attention, and the increase in the wrist Vpeak was associated with an same applies both to strength and to the rate of increase in both Vpeak and displacement (Disp) in all force development of the muscle groups involved joints (Dunbar, et al., 2012). However, note also that (Mirkov, Nedeljkovic, Milanovic, & Jaric, 2004). the most prominent increase in Disp was observed in Regarding punching per se, one could be also inter- the hip joint of ipsilateral leg. For example, the rela- ested in effectiveness of the tested punch regarding tive increase of Disp of the hip in all the three exper- its impact speed, effective mass, and, consequently, imental groups was close to 40%, while the same the associated momentum. Third, although we increase in other three joints was typically below detected signifcant effects of the applied training 10% (see Figure 2). As a result, one could conclude program on both the kinematic and kinetic varia- that the observed increase in Disp and, consequently, bles, the groups were perhaps too small to identify Vpeak could largely originate from a more pronounced the differences among them. Nevertheless, we ran pelvis motion (Cabral, et al., 2010; Cheraghi, et al., a post-hoc statistical power analysis regarding the 2014; Szymanski, et al., 2007). Another mechanism differences in percent increase in performance and

84 Markovic, P. et al.: EFFECTS OF TRAINING AGAINST ELASTIC RESISTANCE... Kinesiology 48(2016)1:79-86 other variables observed across the three experi- rately explore the role of both load magnitude and mental groups and typically obtained sample sizes alteration of kinematic and kinetic patterns associ- of above 30 participants per group needed to detect ated with the applied ERT training. Regarding the signifcant differences among them. Finally, both punching task per se, both the velocity of the hand the optimum magnitude of the applied load and the at the instant of real impact and the effective mass rate of its increase over the course of the applied could deserve attention of future studies. training program certainly deserve attention of High performance of rapid open-kinetic chain future studies. movements, such as kicking, throwing, hitting, or To conclude, the results revealed that a rela- punching, is an important prerequisite for success tively small amount of ERT added to a regular in various sports. We found that a moderate amount training program could be effective in the enhance- of jab punching practice against elastic resistance, ment of jab punch performance even in highly added to the standard training routines, could mark- trained athletes. The enhancement was observed edly improve punching performance (i.e. hand peak in an increase of both velocity and displacement of velocity) in young elite competitors in various the hand and it could be considerably based on the combat sports. That improvement is probably based altered movement pattern (particularly regarding an mainly on larger displacements without any penalty increased involvement of the pelvic movement), as in terms of prolonged movement time, although the well as on the increased strength of agonist muscles. increased muscle strength of the agonist muscles No differences among the athletes already special- could also play a role in it. Therefore, an addition of ized in KB, SB, and BO were recorded regarding the a relatively small amount of training against elastic observed outcomes. Future studies could explore to loads could be recommended for the purposes of which extent the obtained fnding could be extended increasing performance of the rapid limb move- to other important open-kinetic chain movements ment even in athletes of a relatively high level of (e.g. throwing, kicking, etc.), as well as more elabo- profciency.

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Submitted: May 7, 2015 Correspondence to: Accepted: April 13, 2016 Slobodan Jaric, Ph.D. Human Performance Lab, University of Delaware Rust Ice Arena, Rm. 153, 549 S. College Ave. Newark, DE 19716, USA Phone: +1-302-8316174 Fax: +1-302-8313693 E-mail: [email protected]

Disclosure statement: No funding was received for this work from any of the following organizations: National Insti- tutes of Health (NIH); Wellcome Trust; Howard Hughes Medical Institute (HHMI), or other(s).